No mods are required. But... Here is what I've done with mine.
I got some 1" (or 3/4"?) expanded metal from the big box home repair store to lay on top of the charcoal grate. I use lump and it helps to keep the smaller pieces from falling through.
I put a bead of high temperature silicone along the groove on the bottom joint on the middle section to provide better sealing.
I installed one eyelet for routing temperature probes. You can buy a very nice hollow bolt that does this but I just got brass eyelets for much less at the H/W store.
I added some short bolts midway between the bottom and top racks that I can set an additional 18" rack on. For stuff that's not too tall like chicken legs or ribs lying flat it gives me 50% more cooking surface.
I didn't put casters on mine because my brick patio is too uneven to make them useful. Nor have I bothered to add handles to the midsection.
Other popular mods are to substitute a clay pan for the water pan (and use it dry, I think.) I haven't done that either. I recommend trying a couple smokes with the water pan used as intended to hone your skills at temperature control before you try that if you are so inclined.
The mod I most highly recommend is a few hot coals on top of a bed of charcoal and smoking wood (search for Minion method) in the bottom and a couple butts or racks of ribs - properly seasoned - on the grates. Remove when done and enjoy!